The Dynamic Host Configuration Protocol (DHCP) enables a DHCP server to assign an Internet Protocol (IP) network address to a DHCP client. A description of DHCP is provided in a publication entitled “RFC 2131—Dynamic Host Configuration Protocol” by R. Droms, Bucknell University, dated March 1997, the teachings of which are hereby incorporated by reference in their entirety. Additionally, a description of how two DHCP servers achieve synchronization for high availability DHCP service is provided in a publication entitled “DHCP Failover Protocol” by Droms et al., Proceedings of the Fifty-Sixth Internet Engineering Task Force, dated March 2003, the teachings of which are hereby incorporated by reference in their entirety.
In some situations, DHCP Relay Agents are useful for conveying DHCP messages between DHCP clients and DHCP servers (e.g., across subnets). During DHCP message exchanges, the DHCP Relay Agents are capable of sending additional information to the DHCP servers. A detailed description of the Relay Agent Information Option is provided in a publication entitled “RFC 3046—DHCP Relay Agent Information Option” by M. Patrick, dated January 2001, the teachings of which are hereby incorporated by reference in their entirety.
If DHCP version 4 (DHCPv4) Relay Agents lose their state information about ongoing DHCPv4 conversations (e.g., due to temporary power failure, software outages, etc.), the DHCPv4 Relay Agents can issue DHCPLEASEQUERY messages to the DHCP servers in attempts to recover their state information. The DHCP servers respond as quickly as possible to the DHCPLEASEQUERY messages with responses (e.g., DHCPLEASEACTIVE, DHCPLEASEUNKNOWN or DHCPLEASEUNASSIGNED messages) to enable the DHCP Relay Agents to determine the status, IP endpoint locations and remaining durations of IP network address leases. Once a DHCP Relay Agent receives a response to a particular DHCP leasequery, the DHCP Relay Agent updates its state information so that it can resume providing service. A detailed description of DHCPLEASEQUERY messages is provided in a publication entitled “RFC 4388—Dynamic Host Configuration Protocol (DHCP) Leasequery” by R. Woundy and K. Kinnear, dated February 2006, the teachings of which are hereby incorporated by reference in their entirety.